Accelerator admixture

ABSTRACT

An accelerator composition for use with sprayed cementitious compositions, which is an aqueous solution or dispersion of a blend of the essential Components 1–3
     Component 1—aluminium sulphate   Component 2—at least one of an alkanolamine and an alkylene diamine or triamine   Component 3—hydrofluoric acid
 
optionally with at least one of Components 4–7, with the proviso that at least one of Component 4 or Component 5 be present:
   Component 4—at least one of sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, lithium carbonate, sodium carbonate, potassium carbonate, magnesium carbonate, sodium sulphate, potassium sulphate, magnesium sulphate and lithium sulphate;   Component 5—C 1 –C 10  aliphatic mono- and dicarboxylic acids and their metal salts;   Component 6—aluminium hydroxide;   Component 7—at least one of phosphoric acid and phosphorous acid.   

     The accelerators have excellent long-term stability and work well with “difficult” cements, such as some Japanese OPCs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of InternationalApplication No. PCT/EP2004/001594, filed Feb. 19, 2004, which claims thebenefit of Application No. GB 0304158.9, filed Feb. 25, 2003 from whichapplications priority is claimed.

This invention relates to low alkali and alkali-free accelerators forsprayed cementitious compositions.

The use in cementitious compositions such as concrete to be applied byspraying of low alkali and alkali-free accelerators in place of thetraditional aluminates and other strongly alkaline materials is now wellestablished. The major components of such accelerators are aluminiumcompounds, the most commonly encountered being aluminium sulphate andamorphous aluminium hydroxide. In addition to these aluminium compounds,a variety of other components have been used in such accelerators, theseincluding alkanolamines, other aluminium salts (such as oxalates andnitrates) and various organic acids. More recent compositions haveinvolved the use of fluoride ions.

The major problem in the art is to find an accelerator composition thatcombines acceptable performance, acceptable stability and an acceptablecompressive strength. Stability can be a problem, especially in the moreextreme conditions sometimes encountered in tunnels, and a reasonableshelf-life is necessary for a practical accelerator. All acceleratorsused in spraying concrete lower the compressive strength compared to thecompressive strength of the same concrete without accelerator. It isnecessary that this lowering be kept to a minimum. In addition, a goodearly strength development in the 1–4 hour period after spraying isparticularly desired.

In addition, the worldwide variation in cement types causes problems.What works well with one cement in, say, Europe will not necessarilywork so well with an Australian or a Japanese cement. It is difficult toformulate an accelerator that will work acceptably well with all types.

It has now been found that a particular combination of materials givesan accelerator that performs especially well and is very stable. Theinvention therefore provides an accelerator composition adapted to beused with sprayed cementitious compositions, which is an aqueoussolution or dispersion of a blend of the essential Components 1–3:

-   Component 1—aluminium sulphate-   Component 2—at least one of an alkanolamine and an alkylene diamine    or triamine-   Component 3—hydrofluoric acid    optionally with at least one of Components 4–7, with the proviso    that at least one of Component 4 or Component 5 be present;-   Component 4—at least one of sodium hydroxide, potassium hydroxide,    lithium hydroxide, magnesium hydroxide, lithium carbonate, sodium    carbonate, potassium carbonate, magnesium carbonate, sodium    sulphate, potassium sulphate, magnesium sulphate and lithium    sulphate;-   Component 5—C₁–C₁₀ aliphatic mono- and dicarboxylic acids and their    metal salts;-   Component 6—aluminium hydroxide;-   Component 7—at least one of phosphoric acid and phosphorous acid    the ingredients being present in the following proportions (active    ingredients by weight);-   Component 1—from 30 to 60%, calculated on the basis of 17% aluminium    sulphate;-   Component 2—from 0.1 to 15%,-   Component 3—from 0.2 to 8.0%-   Component 4—up to 15%-   Component 5—up to 15%-   Component 6—up to 15%-   Component 7—up to 5%.

Component 1, aluminium sulphate, may be any aluminium sulphate used inthe manufacture of accelerators. It may be fully hydrated, or totally orpartially calcined. A typical grade, and the one on which the proportionis based, is “17%” aluminium sulphate (Al₂(SO₄)₃.14.3H₂O) (called thusbecause that is the proportion of aluminium oxide therein). should anyother aluminium sulphate be required, he appropriate quantity can beeasily calculated on this basis. Preferably Component 1 is present inthe proportion of from 30–46% by weight of the total acceleratorcomposition.

Component 2,alkanolamine, alkylene diamine and alkylene triamine may beany such material, but is preferably ethylene diamine, ethylenetriamine, diethanolamine or triethanolamine, most preferablydiethanolamine. It is preferably present in the proportion of from0.1–10%, more preferably from 0.1–8%, by weight of the total acceleratorcomposition. It is possible to use a combination of two or more of suchmaterials.

Component 3, hydrofluoric acid is generally used as an aqueous solutionof about 40% HF by weight. The proportion of hydrofluoric acid presentin the total accelerator composition (as HF) is preferably from 2–4% byweight of the total accelerator.

Component 4 may be selected from among the materials previously named.Although sodium and potassium are alkali metals, the proportion of suchmetals in the accelerator compositions according to this invention maybe sufficiently low to permit these accelerators to be considered asalkali-free according to the accepted European definition (lower than 1%(weight) of Na₂O equivalent). Up to 8.5% Na₂O equivalent is considered“low alkali” and is acceptable for many purposes—in many cases, rigorousexclusion of alkali on health and environmental grounds is not necessaryand a small proportion of at least one alkali metal enhances the earlystrength development. Thus, for the purposes of this invention, andcontrary to the current practices of the art with respect to alkali-freeaccelerators, it is preferred that a minor proportion of alkali metal bepresent. This proportion is preferably no higher than 5% Na₂Oequivalent. The preferred proportion of Component 4 is from 1–10% byweight of the total accelerator composition. Component 4 is typicallyadded to the accelerator composition as a 30% weight solution in water.

Component 5 may be selected from one or more of the group of acids.Especially preferred are formic, oxalic and glycolic acids and theirmetal salts, but other acids, such as acetic, propionic, succinic,citric and tartaric acids are also useful. Preferred proportions ofComponent 5 are from 2–10%, more preferably from 4–8%, by weight of thetotal accelerator composition.

It is required that at least one of Component 4 and Component 5 bepresent in the composition. The preferred Components 4 and/or 5 for thepurposes of this invention are sodium oxalate, potassium oxalate andmixtures of one or both of these with lithium hydroxide. TheLiOH/sodium-potassium oxalate mixtures are particularly preferred.

Component 6, aluminium hydroxide, is preferably amorphous aluminiumhydroxide of the type normally used in accelerators for sprayedconcrete. It is preferably present in the proportion of up to 10% byweight of the total accelerator composition. It is possible to usecrystalline aluminium hydroxide; this is considerably cheaper, but it isdifficult to dissolve and it does not perform as well as the amorphousmaterial.

Component 7, phosphoric acid (H₃PO₄) or phosphorous acid (H₃PO₃), actsas a stabiliser. Although it is possible to omit it, it confers a usefuldegree of stability on the accelerator compositions of this invention, avital consideration in tunnelling operations where the accelerator mayhave to remain in a ready-to-use state for long periods. It is thereforepreferably present, and in a concentration of from 0.1–2% by weight ofthe accelerator composition. It is possible to use a blend of bothacids, but it is preferred to use phosphoric acid alone.

The accelerator compositions may be prepared by simply mixing theabovementioned components in any order and stirring to give an aqueoussolution. In some cases, additional water will need to be added. Thefinal composition will generally comprise from 40–70% by weight ofwater.

Given the nature of the ingredients, the resulting acceleratorcomposition will not be a simple mixture of ingredients but a complexblend of reaction products. For example, the HF will react with someother components (most especially aluminium hydroxide, if any bepresent). This composition is very stable, having a shelf life undernormal storage conditions of several months.

In use, the accelerator composition of the invention is injected at aspray nozzle in the conventional manner. The dose is typically from5–12% by weight accelerator composition based on cement weight. Theinvention also provides a method of applying a cementitious compositionto a substrate by spraying, comprising the steps of mixing a batch offluid cementitious composition and conveying it to a spray nozzle, therebeing injected at the nozzle an accelerator as hereinabove described.

Sprayed cementitious compositions that utilise accelerator compositionsaccording to this invention exhibit an unusually rapid build-up ofcompressive strength. In addition, the accelerator compositions workwell with an unusually wide variety of cements, including Japanesecements, with which other alkali-free accelerators give lesssatisfactory results. The invention also provides a hardenedcementitious layer applied to a substrate by spraying through a spraynozzle, there having been added at the nozzle an accelerator ashereinabove described.

The invention is further illustrated by the following non-limitingexamples in which all parts are by weight.

A number of accelerators are added to a test mortar mix having thefollowing constitution:

water 198 parts ordinary Portland cement 450 parts sand (DIN 196-1) 1350parts superplasticiser 2.7 parts

The cement is Tayheiyo OPC, a commonly-used Japanese cement. Thesuperplasticiser used is NT-1000 ex NMB Ltd., Japan.

EXAMPLE 1

To the abovementioned mix is added with thorough mixing 31.5 parts of anaccelerator according to the invention and having the followingcomposition (given as percentages by weight):

aluminium sulphate (16H₂O) 35 diethanolamine 2.1 sodium sulphate 11.2oxalic acid 7.5 hydrofluoric acid 6 amorphous aluminium hydroxide 9.5water to 100%

EXAMPLE 2

Example 1 is repeated, with the exception that the 31.5 parts of theaccelerator according to the invention is replaced by acommercially-available alkali-free accelerator sold as MEYCO® SA162.

EXAMPLE 3

Example 1 is repeated, with the exception that the 31.5 parts of theaccelerator according to the invention is replaced by acommercially-available alkali-free accelerator sold as MEYCO® SA170.

The samples are tested for compressive strength according to prEN(preliminary European Standard) 12394 and the results obtained are shownbelow:

Compressive strength (MPa) at Example No. 6 h 1 d 7 d 1 3.6 20.1 39 21.4 1.8 23.2 3 0.8 8.6 28.9

It can be seen that the composition comprising the accelerator accordingto the invention develops compressive strength earlier than thecompositions comprising the commercial accelerators, and that the finalstrength is substantially higher.

1. An accelerator composition adapted to be used with sprayedcementitious compositions, comprising an aqueous solution or dispersionof a blend of Components 1–4: Component 1—aluminium sulphate Component2—at least one of an alkanolamine, an alkylene diamine or alkylenetriamine Component 3—hydrofluoric acid Component 4—at least one ofsodium hydroxide, potassium hydroxide, lithium hydroxide, magnesiumhydroxide, lithium carbonate, sodium carbonate, potassium carbonate,magnesium carbonate, sodium sulphate, potassium sulphate, magnesiumsulphate or lithium sulphate; Optionally with at least one of Components5–7: Component 5—at least one of C₁–C₁₀ aliphatic mono-carboxylic acids,C₁–C₁₀ aliphatic dicarboxylic acids or their metal salts; Component6—aluminium hydroxide; or Component 7—at least one of phosphoric acid orphosphorous acid; the components being present in the followingproportions (active ingredients by weight of total acceleratorcomposition) and having an alkali metal equivalent content greater than1% Na₂O equivalent; Component 1—from 30% to 60%, calculated on the basisof Al₂(SO₄)₃.14.3H₂O; Component 2—from 0.1% to 15% Component 3—from 0.2%to 8% Component 4—greater than 0% to 15% Component 5—up to 15% Component6—up to 15% Component 7—up to 5%.
 2. An accelerator compositionaccording to claim 1, in which Component 4 contains alkali metal and ispresent to the extent that the alkali metal content is greater than 1 upto a maximum of 8.5% Na₂O equivalent.
 3. An accelerator compositionaccording to claim 1, wherein the aluminium sulphate is at least one offull hydrated, partially calcined or totally calcined.
 4. An acceleratorcomposition according to claim 1, wherein Component 2 is at least one ofethylene diamine, ethylene triamine, diethanolamine or triethanolamine.5. An accelerator composition according to claim 1, wherein Component 2is present in an amount of from 0.1% to 10% by weight of the totalaccelerator composition.
 6. An accelerator composition according toclaim 1, wherein hydrofluoric acid is present in an amount of from 2% to4% by weight of the total accelerator composition.
 7. An acceleratorcomposition according to claim 1, wherein Component 4 contains alkalimetal and is present to the extent that the alkali metal content isgreater than 1 up to a maximum of 5% Na₂O equivalent.
 8. An acceleratorcomposition according to claim 1, wherein Component 4 is present in anamount from 1% to 10% by weight of the total accelerator composition. 9.An accelerator composition according to claim 1, wherein Component 4comprises a solution in water.
 10. An accelerator composition accordingto claim 1, wherein Component 5 is at least one of formic acid, oxalicacid, glycolic acid, acetic acid, propionic acid, succinic acid, citricacid, tartaric acid, or metal salts thereof.
 11. An acceleratorcomposition according to claim 10, wherein Component 5 is at least oneof sodium oxalate, potassium oxalate, or mixtures of one or both withlithium hydroxide.
 12. An accelerator composition according to claim 1,wherein Component 5 is present in an amount of from 2% to 10% by weightof the total accelerator composition.
 13. An accelerator compositionaccording to claim 1, wherein Component 6 is at least one of amorphousaluminium hydroxide or crystalline aluminium hydroxide.
 14. Anaccelerator composition according to claim 1, wherein Component 6 ispresent in an amount of up to 10% by weight of the total acceleratorcomposition.
 15. An accelerator composition according to claim 1,wherein Component 7 is present in an amount of from 0.1% to 2% by weightof the total accelerator composition.
 16. A method of applying acementitious composition comprising cement to a substrate by spraying,comprising the steps of mixing a batch of fluid cementitious compositionand conveying it to a spray nozzle, there being injected at the nozzlean accelerator according to claim
 1. 17. The method of claim 16 whereinthe accelerator composition is injected in a dose from 5% to 12% byweight of accelerator composition based on cement weight.
 18. A hardenedcementitious layer applied to a substrate by spraying through a spraynozzle, there having been added at the nozzle an accelerator accordingto claim 1.